Microbial expression systems have numerous advantages for the production of useful proteins. While certain microbial systems are useful for producing simple proteins, such microbial systems would need to be improved for the efficient production of more complex proteins. The improvement of microbial cell specific productivities requires complex engineering, and substantial understanding and rewiring of the underlying microbial metabolism. An ideal strain would be genetically stable, have a high specific and volumetric productivity, form no by-products, and use a well-defined medium. These characteristics would allow for downstream processing with a limited number of steps.
Labyrinthulomycetes are robustly fermentable eukaryotic microalgae. These heterotrophic microorganisms are recognized for their industrial ability to consume sugar and store large amounts of cellular oils as triglycerides; the most commercially important is docosahexaenoic acid (DHA), an omega-3 polyunsaturated fatty acid (PUFA) that is a major component of fish oil. These organisms produce oils that can be used in human and animal nutritional supplements, as well as for food fortification applications. These triglyceride oils can be produced in culture using inexpensive media.
Because of these desirable qualities it would be advantageous to have recombinant Labyrinthulomycetes cells that are able to produce a variety of proteins or therapeutic proteins, including therapeutic proteins and functional antibodies.
Many therapeutic proteins require N-linked glycosylation to function, optimally. The human pathway for synthesizing N-linked glycans differs from those of other mammals, invertebrates, plants, insects, and lower eukaryotes (such as yeast of fungi). This presents a problem when attempting to express human proteins in heterologous hosts, namely that the protein of interest will not contain human N-linked glycans, but instead be decorated with N-linked glycans that are endogenous to the heterologous host. This can result in a myriad of problems ranging from proteins that are allergenic, less active, inactive, less soluble, insoluble, unstable, unable to properly interact with biological targets. It would therefore be very useful to have a heterologous host system that is able to produce proteins containing human patterns of glycosylation or simplified glycosylation patterns that could be easily converted into human patterns.